The present invention relates to systems for removal of arsenic from water, and more specifically from municipal or rural water systems, utilizing magnesium hydroxide doped with a divalent or trivalent metal cation as an adsorbent for arsenic.
The presence of arsenic in drinking water is a significant health concern. Chronic exposure to arsenic has been linked to cancer. The current drinking water regulations by the United States Environmental Protection Agency set the maximum contamination limit (MCL) of arsenic at 10 parts per billion (ppb). By reducing arsenic exposure, the risk of cancer is reduced. The presence of arsenic in drinking water in excess of the MCL affects many municipal water systems across the United States, particularly those drawing from ground water sources. Effective and efficient removal of arsenic from drinking water is of primary concern. Ground water obtained from areas with geologic evidence of volcanic activity, both high arsenic levels and high mineral content, including carbonates, are generally problematic. Current technologies are less effective for influent water that contains minerals, including carbonates. There have been a number of systems used to remove arsenic and other heavy metals from water, including reverse osmosis, column purification, and hydroxide precipitation. Many of these processes provide acceptable results only within narrow and restrictive parameters and are highly dependent on site-specific water chemistry. Due to this inefficiency, many of these processes are costly and comparatively inefficient.
None of the prior systems meet the requirements of efficient removal of arsenic utilizing commonly and inexpensively available reagents with a minimum of mechanical processing and steps. Thus there is a need for an inexpensive and simple process that specifically removes arsenic from drinking water, in the presence of other minerals.
In addition to the treatment of water to remove arsenic, quantitative measurement of arsenic concentration in water at 1-50 ppb levels requires expensive and complex equipment that is not feasible for small and medium-sized municipal water treatment facilities. Thus, there is a need for a system for concentrating arsenic from less than 50 ppb to higher, more easily detectable concentrations in water (preferably by a factor of at least 10 to 30 times). Detection of arsenic at a 100 ppb level and above allows for less expensive equipment and less complex techniques to be used for arsenic quantification.